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authorLi Zefan2013-01-24 00:43:28 -0600
committerGreg Kroah-Hartman2013-03-03 16:09:07 -0600
commitcc0e3e13b0a90e5ff42d5b134939eacf5e7e497c (patch)
tree9c755b28f50082b772b96ee2b14514f977f8f031
parent6403d47ff9392807fcfa4464527193e0cab65b2a (diff)
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cgroup: fix exit() vs rmdir() race
commit 71b5707e119653039e6e95213f00479668c79b75 upstream. In cgroup_exit() put_css_set_taskexit() is called without any lock, which might lead to accessing a freed cgroup: thread1 thread2 --------------------------------------------- exit() cgroup_exit() put_css_set_taskexit() atomic_dec(cgrp->count); rmdir(); /* not safe !! */ check_for_release(cgrp); rcu_read_lock() can be used to make sure the cgroup is alive. Signed-off-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/cgroup.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1749dcd976b..b964f9e406f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -359,12 +359,20 @@ static void __put_css_set(struct css_set *cg, int taskexit)
359 struct cgroup *cgrp = link->cgrp; 359 struct cgroup *cgrp = link->cgrp;
360 list_del(&link->cg_link_list); 360 list_del(&link->cg_link_list);
361 list_del(&link->cgrp_link_list); 361 list_del(&link->cgrp_link_list);
362
363 /*
364 * We may not be holding cgroup_mutex, and if cgrp->count is
365 * dropped to 0 the cgroup can be destroyed at any time, hence
366 * rcu_read_lock is used to keep it alive.
367 */
368 rcu_read_lock();
362 if (atomic_dec_and_test(&cgrp->count) && 369 if (atomic_dec_and_test(&cgrp->count) &&
363 notify_on_release(cgrp)) { 370 notify_on_release(cgrp)) {
364 if (taskexit) 371 if (taskexit)
365 set_bit(CGRP_RELEASABLE, &cgrp->flags); 372 set_bit(CGRP_RELEASABLE, &cgrp->flags);
366 check_for_release(cgrp); 373 check_for_release(cgrp);
367 } 374 }
375 rcu_read_unlock();
368 376
369 kfree(link); 377 kfree(link);
370 } 378 }